In the typical prior art process for metal winning, often a first step involves the combination of a caustic reagent such as sodium hydroxide in a high temperature digestion (e.g., autoclave) to solubilize valuable components of a metal source. Such sodium hydroxide processing causes problems related to the difficulty in separating metal species and problems relating to the nature of metal silicate materials produced during the solubilization process.
Since all metals are solubilized in the reaction into a typically sodium metalate form, different metals can be difficult to separate due to the fact that many valuable metals in the transition metal groupings having similar properties are difficult to separate efficiently. Further, the water soluble silicates formed in the processes may form polymeric silica gels, which can substantially inhibit the processability of the solubilized metalate. Additionally, ion exchange columns used in downstream processing can be irreparably harmed by silica that can bind to the resin irreversibly. As a result, sodium hydroxide solubilization processes require substantial intermediate purification to separate valuable metal species from other species in the mixture and to remove silicates from the reaction mixture prior to downstream processing.
Still further, the sodium solubilization metalate processes of the prior art do not lend themselves to winning metal from low grade sources. It is not a commercially viable process to produce tungsten or other transition metals from low grade sources since the concentration of the metal is so low and the resulting by-products from the sodium hydroxide digestion interfere with downstream processing, so that the overall cost of processing does not justify the use of low grade sources.
Downey et al., U.S. Pat. No. 5,882,620, suggest a direct pyrometallurgical process for forming tungsten carbide. While such direct high temperature processes can have some applicability to purification of tungsten, they are difficult to carry out with low grade ore. Further, the process does not work with many metals well enough to realize substantial commercially viable success.
Sodium tungstate is often formed in metal winning processes. However, the use of sodium tungstate or sodium metalates in high temperature fusion chemistry is not known.
In prior art processes for producing sodium tungstate, traditional sources of tungsten, typically tungsten ore, are crushed, milled and sized to a useful size. Often a sulfide float is used to remove copper and bismuth from the raw ore. The crushed ore is separated into a −40 mesh portion that is 70% tungsten oxide which can be further refined. The larger size material is then magnetically separated to remove iron and other ferromagnetic materials leaving a 72% tungsten ore. That ore is then typically combined with a strong base such as NaOH to form a sodium tungstate solution which is then filtered. Silicates are precipitated from solution. The filtrate is solvent extracted with an ammonium reagent to form ammonium paratungstate which is then crystallized and then ultimately reduced with hydrogen. Hydrogen reduction forms tungsten metal by contacting tungsten with hydrogen at high temperature.
While this traditional process produces tungsten metal, a significant problem exists at the stage where the tungsten oxide intermediate product is contacted with a strong base. That strong base tends to dissolve all of the metal containing input material leaving a sodium tungstate solution containing a variety of calcium, magnesium and other impurities that are brought forward in the process sequence. While silicates and some other materials are precipitated, the material remains somewhat impure.
A substantial need exists to obtain a tungsten purification system that obtains a substantially purified sodium tungstate that can be further processed into tungsten metal. Further, substantial need exists in learning to use molten sodium metalate phases as solvents or processable liquid materials. Finally, a substantial need exists in using fusion processes to form vitreous structures wherein particulate material, such as radioactive waste products, can be encapsulated and held within the vitreous structure.